(1) Field of the Invention
The present invention relates to an image signal processing device and an image signal processing method.
(2) Description of the Related Art
As a related art of the present technical field, there is Japanese Patent Application Laid-Open 2007-318256, for example. The present patent document describes in its abstract of the disclosure as follows: “An image correction circuit capable of easily realizing adaptive color correction taking into account a luminance correction amount is provided. A gamma-correction circuit 21 applies luminance correction (contrast improving) to an input luminance signal Yin. Using an amount of luminance correction ΔY, a chrominance correction unit 3 performs chrominance correction on the basis of prescribed expression. Adaptive color correction interlocked with the amount of luminance correction ΔY in the gamma-correction circuit 21 is realized. Furthermore, a denominator of the amount of luminance correction ΔY is assumed to be fixed value L. Thereby, the circuit configuration is not made complicated. Furthermore, even in the case that, e.g. the amount of luminance correction ΔY and the degree of adaptive color correction K are greater than required, it is avoided that color difference signals Uout and Vout after the chrominance correction become excessive, by means of the fixed value L being the denominator of ΔY and the degree of adaptive color correction M satisfying 0<M=3.”
As another related art of the present technical field, there is Japanese Patent Application Laid-Open 2000-156871, for example. The present patent document describes in its abstract of the disclosure as follows: “The present invention relates to an image processing device and an image processing method, and can be applied to an image processing device mounted in a television receiver, a video tape recorder, a television camera, and a printer, for example, to enable correction of gradation even in a dynamic image by avoiding partial deterioration of contrast effectively. After separating luminance data y (i, j) from image data x (i, j), a correction coefficient g (i, j) is generated based on determination result r (i, j) of an area to which the luminance data y (i, j) belongs, and the pixel value is corrected.”
As a further another related art of the present technical field, there is Japanese Patent Application Laid-Open 2008-263475, for example. The present patent document describes in its abstract of the disclosure as follows: “According to each image, contrast correction is performed appropriately. An input-output characteristics setting unit generates an S-shaped input-output characteristics curve CL21 in which an output contrast component monotonically increases with respect to an input contrast component and a gradient becomes a maximum contrastGain/gamma_comp when the value of the input contrast component is around zero. A gain characteristics calculation unit generates a contrast gain curve indicating the characteristics of a gain value with respect to the input contrast component on the basis of the input-output characteristics curve CL21. A contrast correcting unit corrects the contrast component of each pixel on the basis of the contrast gain curve and a gain value which is calculated based on either the input contrast component or a luminance value. The present invention is applicable, for example, to a digital video camera.”
As a yet another related art of the present technical field, there is Japanese Patent Application Laid-Open 2004-23522, for example. The present patent document describes in its abstract of the disclosure as follows: “An object of the present invention, is to provide a contrast correcting circuit which can reproduce a video of high contrast irrespective of video contents. The contrast correction circuit is provided with a gradation correction unit for correcting gradation of an input video signal, a unit for generating a luminance signal from the input video signal, a unit for dividing one picture into plural areas and calculating a mean value of a luminance signal for each area, a unit to generate a frequency distribution information of brightness based on luminance average value for every area, and a control unit for controlling input-output characteristics of the gradation correction unit based on the frequency distribution information of luminance.”